Musical Fidelity strange noise. HELP

Your problem is either one of two things. When the industry changed over to lead free solder, many manufacturers had some difficulty working with it. MF gear in particular had a rash of "bad" solder joints that caused issues as you describe. The other probable cause would be a tube in the pre-amp section has become noisy or unseated in socket. Open the case up and swap the tubes to the opposite channel. See if that cures the noise or if the noise follows the tube.

Good luck

B

Then the cause is most probably a bad solder joint. I'd send it to Rick at signal Path (last I checked they still are MF service center).