Pump grinding from cold start

[Reality|Bites]

So the last couple of days I've had a grinding sound coming from the pump after the PC has been off all night and the heating has been off.
Is it air trapped in the pump or is the water freezing a little bit?
Turning it off and on again a couple of time fixes the issue but what's causing it? air, cold room temp? dying pump?
I'm using Dr Voights DP Ultra fluid.
pump n grind...

 

[Brizzles]

Sounds like an air pocket building up in the pump when idle, it wwould not get cold enough for the fluid to freeze

 

[Reality|Bites]

I've just done a close inspection there, it's leaking a little from one side of the reservoir, it was fine for months and now?
I've just done a bodge quick fix and stuck some putty into the gap.

 

[clone]

Strip down and clean before you lose your pc.