360 weird idle post belt-service

I had the timing belt replaced on my 360 a few weeks ago and it's exhibiting a weird behavior. At idle, there's a rhythmic waa-waaa-waaa that comes and goes. Since my car is loud (headers, 200cell cats, tubi), it's loud inside. Loud enough that I have not been able to record it on my phone. I've had the car 8 years so it immediately jumped out at me as Not Right. The idle itself is rock solid at 1050 or so. Outside, the car sounds about right, maybe a slight "flat" sound that comes and goes (descriptive words fail me).

The shop is planning to pick the car up on Wednesday but I'm hoping to get some thoughts on this. Obviously, I'm suspicious something went awry with the belt service but I don't know what it could be. Cam timing differences between banks? I do realize sh*t happens and it could have nothing to do with the service.

CEL tripped with an 1123 on the passenger bank. That's related to adaptive fuel trim reaching its limits. I saw this years ago but it went away. I hosed the intake area down with brake cleaner on a cold start w/o effect. Maybe I should replace the original coil packs? Could this be related to the weird sound?

I hooked up my scanner and the driver's side O2 voltage looked low (I don't have a scope for a proper look). Swapped it out with a known good used sensor and that cleared up.

Another weird thing: the IATs don't agree. Sitting in the garage, they diverged by as much as 20F. Since I've never looked at them, I have no idea if this is normal or not.

The car is running really well, it just has this damn noise at idle. Appreciate any thoughts from those who have more experience than me.

 

Thanks Wade. To be clear, the sound isn't mechanical, more like constructive interference from two tones almost at the same pitch. Like a twin engined airplane with the props not-quite in sync.

I'm considering waving them off for now and replacing the (original) coil packs. I neglected to mention that the day I noticed, I ran it up to the shop and the SD3 reported some mis-fires on cylinders 2&3. The technician told me it could be a real problem, or it could just as easily be a low-voltage start. He cleared so we could revisit. I'm just being cheap here: I know I can change them out for a fraction of the cost and then I'll have a good baseline car for them to look at.

Any thoughts about the IATs being different bank to bank?

 

Mitch,
Have you actually experienced that? Because that's my knee-jerk reaction since that's what was just messed with, but I have nothing technical to base it on.

 

Thank you! I have (no kidding) 224 pictures from the work. The timing was clearly altered from start to finish though I just noticed I don't have any pictures showing a degree wheel.

EDIT: I zoomed and snipped before/after of the passenger bank. I see that the cams have multiple drill holes so the exhaust timing is not as dramatically changed as it appeared (to me) at first. Before and after:

 

Thanks for the additional feedback all. Unfortunately, the weather pushed the car pickup back so it will be a bit before I get some additional info. In the meantime (and unrelated to the noise but maybe to the P1123), I have a set of coil packs on the way from the UK.

 

Thanks for the additional thoughts. I've managed to record the sound on my laptop - sort of. It's so loud that it saturates the mic. My phone just throws up its hands - you can't hear it at all. The laptop at least registers something. I'll see about posting it.