Thanks everyone. I agree, the obvious solution is not to take one's hands off the bars. Tires are Conti Force - again, this is the first I noticed this issue in 3000 miles on these tires. Perhaps the front has cupped enough to now start doing this. I'll check the other items as well (loose engine bolts, bearings, adjusting tire pressue), but I happened to have coindidentally ordered new tires before I left on this last trip so hopefully I'll resolve this one way or another. Thanks again and I'll post with an update once I get back into the shop.
Scott