Help for a atypical noise/squeaking after changing timing belt D24TIC

[Bonzo760]

Hi friends and greetings from Italy!

Here is my problem: about a month ago I replaced the SKF-branded timing belt at my trusted mechanic (including the SKF-branded water pump and idler pulley). The model of the kit bought is this: SKF VKMC 01040. On this occasion I also changed all the service belts marked BOSCH. In short, I made a nice service to my beloved 765.
The car drives like a wonder! the only problem is that when the engine rpm are at idle and the engine is hot, a slight noise / squeak coming from the engine is particularly noticeable in the passenger compartment and little from the outside (you need to open the bonnet to hear it better). I went to my mechanic and as he heard the aforementioned noise he told me not to worry. According to him the sound comes from the distribution belt and it is normal, with time and use the belt will no longer make this noise (he says it must stabilize...).
I have traveled no more than 350 km (approximately 220 miles) since changing the timing belt. My dear Volvo (1987) now runs few kilometers, because it is registered as a classic car.
Do you agree with my mechanic's analysis?

I thank you all in advance and greet you cordially.