I have acquired a 2247A that is in great shape. However, the fan is noisy and I am wondering if this isAlthough this is probably not the cause of your noise problem this info may be useful anyway:
In Nov 1991 there was a no-charge update kit announced to replace the fan in the 224x series.
Here's a part of the update plan text:
The Sunon brand fans used in the 224X GPS family of scopes have proved
to be less reliable than desired. It appears that after about one
year of use, the rubber O-Rings may wear out and cause the fan to fail
in some products. Although the failure rate has not been excessive
yet, the fan is the highest failing part in those products.
This update program has been, set up to improve the reliability of the
224x scopes by replacing the Sunon fan with the NIDEC brand fan
similiar to that used in 2400 Series Analog scopes.
Every 224X series scope in the listed serial number ranges that comes
in to a service center for any repair and/or calibration should have
the fan replaced, using the 045-0204-00 mod kit.
224x scopes shipped below the listed serial number range do not have
to have the fan replaced. The fan used in the early serial numbered
products was made by AROMAT and has not shown any reliability problems.
Self-service customers that change any of the fans in the 224X scopes
should be instructed to use the 119-2102-01 as a direct replacement.
U.S. Mfg S/M Range:
2245A: B021238 - B032454
2246A: B020327 - &UP
2246 1Y: B710986 - B716415
2246 2Y & MOD A: B111719 - B123563
2247A: B020816 - B031437
2252: B010100 - B022225