Troubleshoot low freq "woof"?

[trans4funks1]

I've got a pair of microphones I plan to tear down and use for mods.

I figured I'd give them a listen before I took them apart.

One of them seemed surprisingly useful as is but the other one ran ok for a short while and then started sounding "woofy". I gave it a "blow test" when it was acting up and that exasperated it but then later I blew on it and it didn't effect the sound adversely. The problem only showed up twice for very short duration but I powered down just in case something might get worse if I didn't.

I had them both set as figure 8 and was using the one that had troubles on vocals and the other on acoustic guitar.

Any ideas on what where to start trouble shooting?

 

[trans4funks1]

Recorded with the pair again and did not have any problems.

Maybe it's just the OEM tube getting used to being a tube?

I'm pleasantly surprised how nice they sound stock and look forward to improving them a bit.