Is it normal for something like the 7500, to hear a hum coming from the unit itself? This is not any type of hum coming from the speakers or anything like that. This is strictly coming from the unit itself. Kind of sounds like a transformer hum or something. It is pretty faint. I can only hear it when there is absolutely no other sound in the living room except the fan on my laptop But, I can hear it from the couch, about 10 feet away. I didn’t think it was the infamous ground loop hum as I thought this would present a noise out of the speakers, and this doesn’t.
Let me know what you guys think.
Thanks.

Whoa, I just noticed something. I have a line conditioner on this outlet too. It clicks and via LED lights, it'll show if it is regulating for a voltage boost or drop. The 7500 was exhibiting the noise more prevalently when the line conditioner showed that there was at the given time a voltage boost which the conditioner was compensating for. When it dropped back down, the hum also dropped.
Looks like I have some troubleshooting/testing to do. I'll try a few different configurations to see if I can notice any patterns.
The problem is I might not always be able to make changes and test since these voltage changes don't always happen in my apartment. Sadly though, they do often.

I had a buzz that developed in my 7700. I traced it to a small Vornado room heater that I have on the same circuit as the 990/7700 units. When I unpluged that small room heater the unit (7700) stopped buzzing.
I would suggest that next time that buzz develops that you start unpluging and or turning off items that are on that same circuit untill you find the culprit as i did.
PapaBear

Okay it was doing it again this evening. I rearranged everything, and no luck. This evening it is fluctuating in its buzz/hum, but unlike before the line conditioner is not displaying any voltage irregularities. It'll have 5 seconds of buzz and then 30 seconds with barely audible or no buzz. I basically have one 2-plug outlet in this corner with what appears to me to be downstream from one light and my computer stuff. Here is what I have done.
- line conditioner unplugged
- line conditioner plugged in downstream from amp (with and without amp on a power strip)
- line conditioner plugged in upstream from amp
(with and without amp on a power strip)
- amp plugged into line conditioner
- unplugged computer system
- turned off upstream light
- unplugged satellite cable from wall
- used cheater adapter on amp

All of these different variations had no effect. Any ideas? Am I just stuck with it like this? I mean, it is not horrible, but I do notice it.

Sometimes, like now, the amp is dead quiet. Weird. I'm wondering if it is noise on the line. If so (but who knows), I'm wondering why my line conditioner didn't help.

Interesting article...
http://www.psaudio.com/products/humbustermoreinfo.asp

jrlouie, Call your local electric co (the folks you pay monthly for elec service) and have them do 3 things. btw: the following is a common occurrence

#1 Tell the elec co that you may be experiencing voltage spikes from a lose connection or lose neutral.

#2 Have them Place a voltage meter, and or a recording voltage meter on your incoming electrical line to the main disconnect or electrical meter on the side of your house. This way they can check for a line voltage spike to your elec box.

#3 Also have the local electric co, go up the power pole and tighten the connections. I can tell you from experience that the connection at the power pole for your main drop to your house can develope a lose connection and this can and will cause a voltage spike on the main line of sometime 10 to 20 volts higher than the other main line if you have a (LOSE NEUTRAL)

Many years ago I designed and constructed cable tv systems from the ground up, and we had a head end full of electronice that keep getting hit from voltage spikes due to a lose neutral.
PapaBear

Jrlouie, One other thing. Be darn sure to disconnect your computers, and other electronics, before they climb the pole. The will cause a voltage spike when they disconnect and reconnect the lines.
PapaBear

Well, I live in an apartment complex. Can I still call the electric company to complain of the spikes? Based upon that link I provided, do you think it could be DC noise on the line? Is it worth buying something like that and trying it out?
People have asked the leasing office about the spikes and brown-outs, but they're just like....well they say we're on this weird grid downtown and there's not much we can do.

Well the electric co is there to provide you service and I would have no problem contacting them to check there line for a lose connection or line voltage that is not equal in to your apt complex from there pole or underground.

Now here is another thing you can do. Get an inexpensive digital voltage meter. Make sure its Digital. Then open your breaker panel (in your apt).
Now dont do this unless your are comfortable with electricty. If you remove the screws to expose the inside of your breaker panel you will see a grounding block with several bare wires and white wires connected to it. Put the black test or common lead on that grounding block. Then you will see to large wires feeding the panel may be a red and black one. Take the other lead (postive one) from your digital meter and touch one of the of the two feeds to the panel and record that # then check the other input and record that#. Mine runs 128.4 on one and 128.0 on the other. Now if you see a fluctuation up or down of several volts or a # like 113 on one side and 143 on the other then you better complain to the electrical co and the landlord. I may be best to chack this on a windy day when wires are blowing in the wind on the electrical co's grid

But if it was me I would contact the elec co 1st and have then insure the line into the building is clean 1st.
papaBear