I am experiencing a high pitch noise from my Trane furnace whenever
the gas flow is open. A repairman said the cause is a high gas
pressure taht the city regulates. This problem only started about a
week ago. The noise would not be much of an issue if the furnace was
not placed in the attic above our master bedroom. Does this diagnosis
sound correct? Is there anything I can do to fix the problem? Should
I get a new furnace (it is only 2.5 years old)?

Thanks.

Is the repair man trying to sell you a new furnace ? , Id call the gas
co Pressure problems can occur and be unsafe.

No, he wasn't trying to sell me a new furnace. But, he said he could
not do anything about it and stated in the repair bill that it was
normal noise.