I have a number of consists with sound and non-sound engines. They all work pretty well, including those with Tsunamis.
It takes an iron man to play with a toy iron horse.
Is the MRC decoder still in the locomotives that make the buzzing sound? The MRC decoders had horrible motor control circuitry and it was practically impossible to speed match them with anything else.
Not sure about the clicking noise. Some club members have had Athearn Genesis locomotives that developed cracked gears, but it's not very common. Athearn does not sell replacement gears for Genesis locomotives as a separate repair part, but does sometimes have replacement wheel/axle/gear sets available.
Speed matching a Tsunami-equipped engine to an engine with a good non-sound decoder isn't a problem. MRC decoders, particularly early ones, aren't generally regarded as 'good' decoders. Replace them with a regular TCS, NCE or Digitrax decoder and they should work fine together.
Sound and NonSound Tsunami's have F11(or whatever other function you may change it to) braking and are great to speed match, even using JMRI. But I speed match them to Digitrax, TCS and other high quality decoders. I'm not crazy about MRC or Bachmann decoders, for lots of reasons so I just replace them vs trying to speed match.
Richard