I never noticed this before, but I don't particularly like it. Is there a way around this? I could probably just route the click to the solo'd bus, but then that'd be extra clicking everytime I solo'd a bus. I have a bus for drums, one for the stereo rhythm guitars and one for all the guitars in general (bass and rhythm)

Do you have a Master bus and a metronome bus also? Typically all the buses are routed out to the Master bus and the Master Bus is routed out to the proper output of the interface (where the speakers get signal from). Also make sure the output in metronome settings is routed to the metronome bus.
 

Your title says "muting" a bus, but it seems you mean "soloing" a bus. Yes if you use a metronome bus, it will be silenced by soloing another bus. You can address that by enabling solo override (Shift-click Solo) on the metronome bus.

brundlefly
Your title says "muting" a bus, but it seems you mean "soloing" a bus. Yes if you use a metronome bus, it will be silenced by soloing another bus. You can address that by enabling solo override (Shift-click Solo) on the metronome bus.

Yes, I meant to say soloing a bus, lol. I had a kid with me so my thinking was shot. But thank you for that solution. I'll try it out later.

Unfortunately, after I posted this, I recalled there's an issue with using solo override on buses that it effectively solos the bus (as opposed to tracks where it has no effect until you solo something else, which is the intent):
 
http://forum.cakewalk.com/Broken-Erroneous-behaviors-Solo-Override-on-buses-m2972299.aspx
 
Ignore all the confusion in the thread by posters who didn't immediately understand the issue. The OP is correct, and later in the thread a Baker says he'll look into it.
 
But this discussion was in reference to X2, and it's still not right.  So not a perfect solution. You might just want to route your metronome direct to Master Buss temporarily.