Welcome to the forum. Lots of info here
There are 6 basic ways to quiet the fan.
1 slap the Opus: may pop out the cells. so not very useful may pop cells out *
2 wd40/silicone spray helps sometimes :smells*
3 Place the Opus on top of a fan sucking the air from the bottom*
4 Replace the internal fan with a quieter fan.
5 replace the fan with external fan connected to the fan switch in the OPus: This is used most often*
6 use remote cell holders connected to the each of the internal cell holders*
* methods I have used.
Later floyd