Recently I've been having a problem in my shack with "buzz saw" RFI noises that seem to come and go, completely, from time to time, both on 11/10 meter and 2 meter. For example, a few days ago I heard some skip coming in on CB Channel 6, so I went to the main shack to give 10 meter SSB a try with my Yaesu 450. Couldn't make any contacts, but could hear plenty on parts of the band I don't have privileges on. Then I turned off the tuner and cruised 11 meter with the 450 to listen in and out of band, hearing endless amounts of Spanish in high quality in AM. All the while, noise ground floor was on the floor, did not even want to read on the S meter. Like other days and times, my CB/10 meter setup is very clean, I can take weak signal very well. Today I hear skip coming in, so I get down to the shack. Even make a contact with a fellow down in Arkansas on CB, short but very clean AM! Excited, I plug in the Yeasu 450 to do work on 10 meter SSB.... only to be greeted with a rhythmic, "buzz saw" RFI pulse, reading 3-4 S units! Disgusted and disappointed, I quit for dinner. I remember that this is the same exact "buzz saw" noise I get on 2 meter FM on weak signal. I started to get this a few weeks ago, and it is sometimes so bad I can't check into the local Canadian net across the border. On 2 meter, the noise is always there, but on the Yaesu 450 it seems to come and go. My Galaxy 2547 didn't suffer the same noise, plugged into the same tuner and feedline and antenna. Minutes before using the 450. The Galaxy isn't currently grounded..... Any help on this issue? Why would such RFI come and go on 10/11 meter? Is it a grounding issue, or ground loop of some sort? The appliances in the shack are few and always on. I've been thinking and looking and I'm stumped. Any help is appreciated.