Hi can anyone out there help me, when using a AC15 with a tube screamer in front just pushing it a tad gain about20 theres a nasty digital tizz in the background as the notes decay.

Its driving me mad, ive tried using the z and runs at 1m with a vintage strat. all of my other models are perfect and dont suffer with this problem.

Even with no tube screamer its still there only slightly less audiable

Thanks