McIntosh C2300 noise

I have a C220.  Although I did not have a severe noise issue like you, I did replace the 4 tubes in this pre with Mullard reproduction 12AX7s, and the preamp got quieter and sounds better in many respects.

I would try this:  If you are using the main single-ended outputs to your amplifier, try using one of the other outputs and see if there is a difference.  I had these outputs fail on both my first C220 and the replacement, which I still have, but use one of the other outputs, not the main one.  As far as I can tell, my long runs of ICs to my amp were stressing the RCA output jacks on the C220, and they failed, resulting in a very loud hum (a short, I guess).  I now suspend the cables to relieve the stress on the C220's output jacks, and have had no issues in about seven years.

Lastly, if your dealer can't figure it out, I have found calls to McIntosh to be answered promptly and helpfully.

@Pistha  - If you had no sources or amp connected to it, how could you hear the buzz?  Is it a transformer hum from within the preamp itself?

^^^^^^Excellent question.

 If you had no sources or amp connected to it, how could you hear the buzz? Is it a transformer hum from within the preamp itself?

the YT video shows no source connected but amp and speakers connected. buzz goes up and down with volume on phono section as seen. As a test - i moved the preamp to a different room with NO source or amp connected. Offcourse I dont hear anything audible as no speakers are connected and no transformer hum either - but the needle jumps as though there is gain/current. So clearly it's not a source or a cable issue. 

If you are using the main single-ended outputs to your amplifier, try using one of the other outputs and see if there is a difference.

@bondmanp - yes - i tried Outputs 1 &2 with same behavior. Differ with you on calling McIntosh - i get very curt responses. Luckily Audioclassics is treating me well!