Is it this badboy?
http://www.sextonsdirect.co.uk/autolead ... html?cat=0
i had 2 of those fitted to mine when I was using the Bose speakers and Amp, 1 for fronts and 1 for rears... the 'Beep' wasn't a problem as I hacked it to silent
It worked fine with the Sub so not sure what your problem is, sounds like it is HU related to me...