I had the same thing with a 15-91 pedal after DH got the machine fixed up. He opened it back up, and it has some condensation inside. Cleaned it up and it still made some funny noises, and DH said it was safe, it was just cooking off the moisture that had been obsorbed by the carbon disks in the pedal.
Since he had opened it up and made sure there was no electrical short, I was OK with using it, and after about 6 hours of use, it settled down and I've not had it repeat that. Who knows how many years it had sat before I started using it, and I've not had another one do it, but I've still got plenty that haven't been put into use yet.
Used the machine to wind 5 bobbins for my quilting machine this morning - no smell or noise. Sure is nice that my Bailey bobbins are about the same size as the 15, so I can use that machine to wind them.