Car question

When I accelerate after coming to a complete stop, my engine (or something) will make a soft grinding noise/growl of sorts. It only happens when I go from zero to about 10 mph then doesn't do it again unless I stop and accelerate. I recently had my front rotors replaced and my air filter for my engine replaced. While I was getting my car fixed the mechanic noticed I had an oil pan leak. Just wondering if this could be the problem or would it be something else?