I bought an SX-70 at an estate sale for a decent price. It looks flawless. I had a used film cartridge with me, and it spit it out just fine. However, the motor sounded a little labored. I haven't had a chance to pick up a new pack of film yet, but I'm curious if anyone else has an SX-70 that sounds like its motor struggles a little.
I have one with a weak sounding motor, it still seems to shoot fine though. It could be a weak battery in your test pack, the terminals need cleaning or the motor is just old and weak. Maybe run it through several more tests and see if it just needs a little exercise after it's long sleep.
Mine sounds like it may not get through 10 shots but keeps chugging along. Come to think of it I remember my grandfather using it at holidays and it pretty much sounded the same 30 years ago.
Probably just weak batteries in the film pack. The PolaPulse battery is a sizeable beast and can last a very long time. My guess is that Polaroid engineers suspected that a pack of film might sit from one Christmas to the next, or longer.
At a swap meet I bought a camera that seemed weak - I made a photo on the spot and it ejected a black and white print from a pack that probably had been in the camera for 10 years. After maybe three minutes, the photo actually developed, though it was faint. The camera has been fine ever since.
It's probably fine, and may just need some exercise.
Just a word of warning... I've had a few packs of Impossible and Polaroid Originals film not eject the first 2 or 3 shots in various cameras. I'd thought it was the cameras, but after a few bouts with a changing bag, I determined it was the pack(s). So if you load some fresh film and have a problem, don't panic. It may be the thicker film.
Clean the rollers and make sure the gears are clean. I had a pod of Impossible film rupture on the first shot, got the blue goo on everything. Pissed me off. Fortunately it was not my gem like original.