series 60 14L Ticking noise/bullgear

I got 2009 westernstar with Detroit series 60 14l DDEC VI .i had overhead adjustment done on the engine.after doing the overhead i started to hear small ticking/chattering noise.mostly you can hear in the cab.its hard to hear it outside.the noise changes as rpm’s go up and down.had my mechanic take look it he’s saying that the noise is from the bullgear. And the reason he said it started doing it after the valve adjustment is that before the valves were out of adjustment and gave enough room for the bull gear to mash in just right with other gears.after adjustment everything got tighter and now the tooth on the bullgear are bit off & not mashing together just right and causing that chattering noise. he is very good mechanic but in this scenario Is not making sense to me.can the bullgear make noise after overhead?truck runs good ,no smoke, no burning oil etc..can someone lead me right direction before i spend 4k on bullgear.

 

Talked to westernstar dealer and they said the exact same things you guys mentioned.taking it to them tomorrow.will definitely let you guys know the result.thanks everyone!!!

 

I made to the dealer pretty late on Friday.so with the holidays they wouldn’t be able to look at til Tuesday.