That is the induction noise going through your pod (yes air being sucked in) (noise is created by the restriction of filter, adding the two will half the restriction of the intake and thus noise)
There are heaps of ways to measure the efficiency of your cooler, start by measuring inlet and outlet temperatures as discussed above using a thermocouple or a pyrometer (that laser thingy:)
1 - (%final - initial)/initial = cooler efficiency
And yes they can be cleaned, do a search on here but im assuming you just pour some particular type of evaporative alcohol inside, swirl and poor out i.e. kero (heaps of black road grime should come out)
Actually if you think about it, the denser air charge (long story short) will cause the turbo to spin faster, air is inducted through the impellor at a faster rate so the pitch will change