Help Needed - Unknown sounds after head gasket replacement. 2010 Daytona 675.

Hey guys, the last time I posted, I said that I needed to replace my head gasket and thermostat. Which I did, it went well and was a hassle but no major issues. I also checked my valve clearances, which were all in spec.

Other things I replaced as well: Thermostat and seal, Changed all the coolant hoses to silicone, New spark plugs, New cylinder head bolts, new rad cap, and a new quick-shifter.

I just finished putting everything back in, and together. But I am having some issues, at first I was having a kinda low idle around 900 - 1000. Also if I lightly revved it, the rpm would drop to around 600 ish then stall. Looked in the forums and found that it was the vacuum line mixed up going into the vacuum tank. Switched them around, and the idle was back to around 1200. Also did a 12 min tune, and that helped it run a bit better. But I still had the issue where I rev it and instead of stalling it just drops the rpm a bit around 200 - 400. So from 1200 idle, rev and now it's 900 ish then it goes back up to 1200. This happens mainly if I twist the throttle quickly and let go or just snap it, if that makes sense. Throughout the rev range, it seems fine.

The map sensor vacuum line is plugged in.

Not sure what is causing this.



Also, I noticed a new sound only when starting, it's hard to describe. But it's almost a hollow ringing sound. You need to listen over the engine cranking to hear it.
This is a video of it:
20230221 205524

It only makes this sound when it's a warm start, not when starting cold. It wasn't doing this before the head gasket replacement or after until now. I've recorded every start after the "rebuild" and it wasn't there. For example, let's say I started it 10 times, I didn't hear anything but normal noises, but on the 11th I hear it and continue to hear it. Hope that made sense.

Also, the engine is harder to start than before, it's taking more turns to start and stutters a bit when starting. Even when up to temp. It did not do this before, at all. Cold or hot, it would start up almost instantly. Not sure what has changed...
Sounds fine when running though.
Here is a video of that:
20230221

Here is a cold-start video to compare:

Any insight would be helpful.

Thanks in advance,

Sebastian