MP2s' aren't fond of bad power (I often run off a generator, in the end I bough an UPS to decouple me and smooth the power supply).
Sounds like a normal MP2 that just needs new tubes and v1.41 EPROM from what you are saying, not that the noise mod won't help (it wasn't invented/conceived for no reason, and I've got 2 kits ready to go...).
So the NR settings are Status:in/out, Mode: Gate/Fader and right arrow to Threshold (when it will kick in), to set select prog edit, NR, (displays status and mode (use right/left buttons to move between each option (Status, Mode, Threshold)), what the arrow points at is what will change with Yes:up/No:down), then store the patch.
so on my old rhythm patch (see MP2 patches) which is now my over the top lead, Status = in, Mode: = Fader, Threshold = 80 and the voice is Ultimate Hi Gain, Drive 70, OD 100, Master 77... The high gain patches in MP2 need the NR mostly for when your not playing LOL. Most of my playing these days is on the Voice 5 Warm Vintage (my current rhythm/lead patch) which doesn't need the NR and is still more distorted than I sometimes want.