Report 147: Sound reports from resident in South Lake Tahoe

At our home south of South Lake Tahoe, we have been hearing tell-tale screams for the last three months. I have several recordings of these screams, and have been in coordination with three of the curators involved with the BFRO for northern California. Suffice it to say that almost nightly, we have been witness to a resounding number of screams/wails which have not been attributable to coyote nor other "known" forms of animal call/sound.  The sounds have occurred from 9:00pm through 7:00am in the morning on a consistent basis.  I have made several recordings, mostly from my bedroom window. We have made several all-night forays into the forest in an attempt to capture the sounds. My brother and I have made extensive backpacking trips into the wilderness surrounding this area in an attempt to pin down the most likely locations for activity, and we feel we have narrowed it down very well (based upon our normal reception of sound and habitational demographic...) I have found tracks in this area which i have photographed as well as "beds" with torn branches/etc. which may very well be attributable to bear activity, although the screams at night are definitely not.  Areas in question are well off of the beaten path. Description:  A mournful wail. Sounds like a locator beacon (like a sonar "ping") usually answered by another of lower pitch, and both seem to converge at some point--after which both cease to sound.  We (my brother and I) have noticed coyote howls interspersed with the "other" sounds.  We have thoroughly explored the areas surrounding our location, some of which our dogs refused to enter.  We've camped out all night with bait, only to give up and head in to hear them after we've been tucked away for a good thirty minutes--leaving us dead tired with no "substantial evidence".