Hello audio equipment creepers, I finally fit the giant Radioshack metal film capacitors into my MXL 991. My mod was based off of this link: Gus' MXL 603 mod. Which I am sure some of you are familiar with. To clarify: I have not replaced the C13 ceramic with a polystyrene yet. The capacitors I have replaced are the same value as described in the mod forum post. Onto the issue at hand--The microphone is working but has this low rumbling sound in the signal. I can make this happen whenever I talk into the capsule at most distances. Additionally, it will come and go without me or a meaningful sound source nearby. So far as I can tell, it has something to do with the capsule; when I remove the capsule this rumbling disappears. Thoughts?