Many years ago I had this with a mower. A friend said tighten the blade. I said it was and he said tighten it again. I did as advised and the the problem was fixed. I doubt that you have anything serious wrong and blades do come loose on occasion.
Check you fuel cap. I’ve seen the vent become restricted where the vent wasn’t completely plugged. As you loosen or remove the cap the air enters and everything will be fine for a few minutes. I’m not sure if you’d hear the air entering the tank. Fuel line, valve issues could also be a...