How about USB-Scopes? Combined with a Laptop, they offer good performance, a lot of memory and quietness.
Some units also offer 8 to 16 Channel Logic-Analyzers.
About moddings the unit: Airflow CAN be a factor in the noise, but the vast majority generally comes from the Fan itself.
Idk what type of fan is installed, but I suspect some 8000 or even 10000RPM 60mm or 40mm fan for about 1€.
Im absolutely sure there are fans on the marker that can deliver similar airflow with a lot less RPM and a lot less noise because of a smaller motor, better design of the fan-blades, a more efficient chassis.
I managed to get my PC both quieter and cooler at the same time by buying better engineered fans. They cost about double to triple what the cheap, noisy ones cost though. But in your case still cheaper than buying a new scope^^