Anyone else have this problem?

I practice a lot with my mouth calls - usually while I'm commuting to work - and I think I've gotten pretty good. I can cutt, purr, yelp, and cut pretty realistically and reliably - but when a bird is responding and coming in, my mouth goes dry and I sound like a rusty spring being bent backwards.

Of course, when a bird is in sight, I generally shut up unless they indicate that they're losing interest - which makes it even more difficult to get a decent sound out - so I find myself resorting to a quick tap to my box call for a cluck.

Any suggestions?