Re-set up my hifi/av system in a new house and have had some issues with two things. These don't occur consistently and I can't seem to put my finger on the underlying cause.

System is:

Espeks, Ekwal, Keilidhs, Linn akurate kontrol, 3 x linn av5125, antimode 8033s II, 2 x BK XXLS400. Linn K600 speaker cable all around and interconnects.

Occasionally when I power up the system there is a crackle/static from the rear surround tweeter. It is not constant in sound or volume level and continues if the preamp is powered off. When it occurs I cannot seem to get rid of it and just unplug the tweeter input. It may happen for several hours and then is perfect again for some time.

Similarly one of the subs develops a hum from the built in amp, nothing untoward from the driver. Again this is intermittent and occurs with the input disconnected and is not effected by the  built in gain setting either. This also self resolves for a period and spontaneously recurs. It is plugged straight in to a wall socket and plugging in to a power strip with TV and media centre makes no difference.

Any suggestions welcome for resolution or further investigation!

I would have to say it is very likely those are both amplifier problems. Speaker drivers can't crackle by themselves (although they can buzz with music if the voice coil is partly burnt). You can try switching channels on the amp to see if the problem switches to the other speaker. If it does then you have an amp problem, probably bad capacitors, that will need to be fixed. Pretty much the same story on the sub - an amp that is failing with bad caps that are on their way out but currently intermittent. Best to get them repaired before they fail completely as they could take out a driver if they fail badly enough.

It turned out to be the powerline adapters that were causing the sub hum. No more unwanted noise from it since they were removed and plugging them back in to the same socket caused the same issue again.

The surround speaker issue is definitely amp related and specifically the treble channel. Switched the treble input to the mid/bass on the speaker terminal and the same issue occurs albeit far more pronounced from the larger driver.

Best just to take it back to the dealer who installed the aktiv cards in all three amps?

Glad you sorted out the sub. Taking it back to the dealer is probably the best bet as it will likely have to go there sooner or later. Of course, Linn is closed now until something like January 3rd they won't be able to get on it immediately.

If you are comfortable with it and want to troubleshoot further you could try switching the Aktiv card from the channel that is acting up to a different channel in the amp. Then reconnect that new channel to the driver to see if the problem goes away. If it does the amplifier channel is at fault, if it stays it is in the Aktiv card which could be sent back to Linn for repair/replacement.