I have noticed that my ButtKicker 2's (2 units) are making what I can only describe as a "motorboarding" vibration at low bass levels (very annoying). When anything of real punch comes through, no problem. This is before ButtKicker had their own amp and I am using a RCA SA-155 to bump the line level signal to a CARVIN DCM-1000 Amp. I have had these for over eight years with no problem until now. I suspect that it may be the RCA Amp has fried but have no way (easily at least) to test. Has anyone had a similar problem? I found a Samson S-Convert Bump Box that appears to be a solution to the RCA Amp. Any insights is appreciated.