[cheshired5]

Ihave a similar age D5 with a touch more mileage and I echo what Lancee says.
The MAF cleaner is CRC MAF Sensor cleaner and is worth waiting a couple of days for from eBay.
If you can't hang on, you can get Halfords Electrical Contact Cleaner off the shelf for £4, although I found it's spray wasn't powerful enough to really blast around the MAF chamber.
When cleaning the MAF, you really need to remove it from the housing using a security torx bit, so you can get good access for the spray.
What's the reason the injector can't be removed?
The knock can be caused by it being incorrectly seated, which is simple to resolve by removing it, scrupulously cleaning the the port and injector body and tip and remounting using a new mounting kit from Volvo for £18.