no, not really. it doesn't sound like you were too sure of your speed though if you were relying on that buzzer. he probably clocked you long before you saw him...
how old was the cop? from what i understand, it takes quite a bit of training and practice to operate radar properly. if you take it to court, the prosecutor will more than likely have the officer describe his training for the judge, as well as the schedule and procedure for calibrating the gun. unless he slips up, you're probably toast. just be adament that you weren't speeding. i wouldn't bring up swerving to avoid that other car unless they ask you about it.
with a prior ticket, i'm not sure how much a laywer is going to be able to help you.