whistling at high speed?

when i'm traveling at 65 or higher on the highway I get a quiet whistle or sometimes humming noise. but if i accelerate down a deserted backroad as quick as i can and then let off i don't hear it. so it's just when i'm cruising that i hear it. i'm pretty sure it's coming from the engine. but it could be the trans or rear diff. has anyone else experienced this and found out what is was. this is in my 82 n/a not the zxt.

another thing. sometimes when i shift from reverse to drive(automatic transmission) something in the transmission hesitates to catch. it's stopped happening when i put more trans fluid in it after i realized it was low(about a week or two ago), but it did it again today.

thanks
pat