Engine noise after belt replacements

I need help.
Over 3 weeks ago I had all 4 belts replaced on my A4 1.8T (not quattro) as it was going on 150,000 km.
About a week later - the car started making noises in third gear when it
hit about 50 km. It is a loudish whining or humming noise and seems to be coming from the passenger side under the hood. I don't know much about cars and called the dealership to report and was told it was just my turbo and that older cars do have more engine noise in the cabin.
Since then friends have been in the car and have also hear the noise -- and as they also know the car they say I am not crazy and this is not right. Sometimes the noise seems to go away when I turn to the left around a curve on the highway. But it is loud and always there at speeds over 50 km. It is there with or without the airconditionoing. I took the car into the dealership frustrated and said to please check this and if they had time to please also change the oil (which it didn't really need yet for another few hundered km - but because leaving my car is an ordeal - I decided to save myself time).
In the end the dealership said they hear nothing at an idle (never even test drove it!!!!) but did change the oil.
They say that they do not "hear" things that are common engine noises that other people think are problems.
I am taking the car back today -- and I am concerned that the same person who changed the belts is going to be looking for problems they may have introduced.
Does anyone have any suggestions to help? I do not know about cars --- but before this loved my little black 98 a4.
R.
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I had too in my 90 000 km service.

After the change I got whirling sound that depended (the pitch of the sound) on the RPM of the engine. It sounded like if the timing belt was too tight.

The sound was not hearable at idle, too.

The problem was in the bearing of the compressor tensioner. As the only tensioner that is adjusted manually it might be sensitive to the load of the belt. The bearing made a sound depending on how tight the belt was tensioned. We got multiple variations in sound depending on the tightness of the belt (continuous whirling vs. whirling only at 3000 rpm).
However, after cleaning and greasing the sound dissappeared but it seems that replacement is needed.
--
Petri Rehtonen

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Thanks ... the dealership has decided that it is my wheel bearings. They are replacing them today. They also suggested I get my front brakes replaced at the same time to save myself money.
I think I will start looking for a new car -- I am not comfortable that this noise started right after the belts were replaced. I don't trust car people. Which is the one thing new car warrantee's have going for them. It is not a question of trust... it is a simple contract fact that they have to support claims on the car. I just thought for some reason Audi would be much better.
Ah well.... I should have posted before I drove back into the dealer. Thank you! R.
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