If you can’t describe the problem any better than that – NO ONE can help you. And bike shop mechanics can’t fix a problem over the phone either. You have to take the bike INTO THE SHOP. I seriously doubt they told you not to come in. What the probably said & you misread them was…”BRING IT IN. We can’t fix it over the phone.”
If it’s some type of cheap bike sold at a discount store, be ready for a shock. It may cost just as much to fix it as you paid for it. I can’t physically SEE the bike via the internet. I can’t physically HEAR the noise you’re talking about.