Yikes, that sounds frustrating.

Ok, so it sounds like the popping is due to the sub's amp repeatedly going in and out of standby mode because it's not getting a signal...

Since it used to work fine, I guess the first thing to consider is if anything in your system has changed recently that could be effecting it. New piece of equipment? A 1 year old messing with your remote control?

Assuming the answer to this is "no", have you checked the connection between the sub and your receiver/pre-amp to be sure it hasn't come loose? Maybe swap the cable?

Have you tried lowering the gain on the sub and increasing the subwoofer trim level on your receiver/pre-amp? I've heard other folks suggest this on the forums in response to similiar situations (i.e., sub was going into standby inapropriately).

What's your crossover set at? What if you raised it so the sub would get or have to reproduce a signal more frequently?