But anyway, I had the same problem as you did with certain freqs. This may sound stupid, but with me, it was the sound reverbriating all the clutter on my desk! I cleaned up my desk and the annoying crap went away. Beleive me, I freaked out at first, sounded like it came from the speaker, did some hunting around to get a "FIX", found out it was my loose change and car keys on my desk. Ive keeped my desk cleaned and have no annoying buss at all. For me it was a DUH!