Seeking Classic Owners: Squeaky Sound During Engine Braking After Service!

I'm facing a weird issue on my RE Classic and I'm hoping someone here might have experienced the same thing, especially after a recent service. During engine braking (when I close the throttle and let the engine slow the bike down), I'm hearing a squeaky sound.

It is definitely NOT the brakes I've checked them thoroughly twice (front and rear). The sound is only present during deceleration via the engine.

The bike just came back from a service, and I'm wondering if something related to the work done (like chain adjustment, lubrication, or a minor component) could be the cause.

Has anyone else on a Classic (or perhaps Meteor/Himalayan) experienced this particular squeaky noise under engine braking post service?