Audio Research VT200 Noise on the Right Channel

Dear Forum,
I bought an Audio Research VT200 with has been fully retubed with KT88 tubes. I didn't notice at the beginning, but a small Noise into the right channel, this noise is like a 50Hz/60Hz noise, and not linked to the Preampl level. It seam more related to the Speaker connection, if the speaker wire is not correctly gripped on the VT200 speaker plug. Seams to be very random.
Any inputs welcome
Thanks in advance
Check that the pin contacts for the output tubes are snug. If not tighten the pin connectors.
Try swapping the tubes from the 'noisy' channel to the 'quite' channel. If the noise follows then you have your answer. I will say that tubes are the first thing to suspect in a tube piece of audio gear with problems.