Spedometer fluctuating

[mcgirl217]

Hello all,
I was driving home today and my spedometer went all the way to zero and then went to 70. I feel I was going 70 on the interstate. I am also noticing a winding noise when it is in park. What do you think it could be? I replaced my thermostat in January and I have been smelling something sweet lately. My coolant doesn't seem to be low but why is it still smelling? I love this car and it has about 96,000 miles and I have only had it since December.
It is a Grand Prix GT Supercharged Engine 2002.

Please help. Thank you,
Kasey

[troy1]

Did the car downshift, buck or surge when the speedo did this?

[mcgirl217]

No,
It just dropped and then went back up again. It never did that before.