I recently had my bike tuned up at my lbs. My bottom bracket was extremely loose and it heavily affected my riding and I didn't have the tool or knowledge to fix it so I sent it in.

They said they put some sort of tape to tighten it up. And for a week or two after, the bike rode like it was new again.

It's been about a month now and every few cranks, I feel a small ding and hear a metal against metal sound. And sometimes, I hear a grinding noise. The bike still rides perfectly fine.

I checked my chainring bolts, chain alignment, chain tension, and they're all fine. My bottom bracket seems to be tight as it should be. Chain is clean and lubed. My spin is good. Everything seems to be fine but the creaks and grinds concern me. Anyone know what's going on? I'd rather know the problem and gain some knowledge instead of sending it to the shop and pay a huge price I might not need to pay for.

Thanks.

They removed one or both crank arms to service your bottom bracket. It is possible for them to loosen up a bit over time and they do make noise when it happens.

Don't be this guy:

I was once that guy

I have the same problem, yet I know everything is tight.

A while ago I was getting similar noises after swapping cranks. I checked if the cranks has any play and there was none, I tightened them a little more anyway and the noise went away. it happens.

Wait...tape???

Yeah I was thinking the same thing. Possibly Teflon tape. I'm pretty sure I wouldnt put that on my BB.

"The use of PTFE tape in tapered pipe threads performs a lubricating function, which more easily allows the threads to be screwed together, to the point of deformation, which is what creates the seal."

I don't want any of the threads on my bike deformed. Just sayin.

That means the tape becomes deformed to create a seal, not the threads.

Still...who uses plumber's tape on a BB?

Yeah, and grease does the same thing. Never heard of a bike shop using teflon tape, seems odd to me.

I've heard it from lots of people (and done it myself) to get rid of creaks froms the BB. It's done with grease, not instead of it. It solved my problem and didn't create others. If there's an issue with it, I'm all ears. It may be more common in the MTB world.

For those who don't know, 'plumber's tape' is thin and meant for threads. It's not like wrapping a BB with packing tape.

Check the bearings in your pedals. It could just be a coincidence that they went bad soon after a service. Probably not the case, but it's worth looking at.