So my smog pump only seems to make noise after my engine gets warmed up. (and no it's not getting masked by other noises). And I just noticed, that's when I start to smell more exhaust gasses too. The noise seems to get slightly louder the longer the engine runs too.

I know bad check valves will lead to a bad smog pump, so I'll probably still replace the smog pump, but would this tend to indicate the check valves are bad?

 

If pump is noisy when hot, the problem is the pump. Check valves are cheap, might as well replace them.