[brent_s]

Definitely sounds like an intermittent connection has developed somewhere. Determining whether it's the driver-amp, amp-receiver, or on the amp circuit board itself is the problem.

Could be as simple as the amp to driver connects shaking loose...they're usually just female quick connectors, which don't always have the best grip and could easily loosen up over time, especially in a subwoofer environment. Pull the driver and crimp 'em good for peace of mind. Check the amp end of the wires as well...usually female quick connectors there too.

After that, confirm the interconnect between amp and receiver. Cables *can* go bad, althought it's uncommon. You could also temporarily use speaker level connections, if available on the sub, to bypass the RCA interconnect. This would deny/confirm the sub's preamp input/RCA interconnect as the culprit.

Advanced troubleshooting. Pull the sub driver and connect the amp straight to one of your main speakers. Still run it as the LFE/sub on your receiver at "safe' levels. If the problem still exists, you've eliminated the driver and probably isolated the problem to the amp board itself.

-Brent