Noise/distortion coming out of speakers

Not sure if this is normal or not. I noticed that when I change the volume, just during that moment, a slight whispering noise (can't find a better way to describe it) comes out of the speakers.
The speakers produce no distortion/interference/noise during the actual music playing, it only happens when I increase or decrease the volume.

Sounds like your volume potentiometer is dirty. There are spray cleaners that will help, but just to be extra safe, I'd ask the manufacturer if it is OK to use that product. (There are some volume pots that are too well sealed so you can't get the spray to where it needs to go.)
Mlsstl sounds like he has the problem nailed. Noisy potentiometer. Look to see if it is a sealed unit or not, if not, a contact cleaner spray can fix the problem right up.
Some volume controls are "self-wiping". We usually only use a small portion of the volume control. Turn the preamp off and turn the volume control all the way from lowest to highest fast several times. That just might clean the contacts off enough to eliminate the noise.
Turning the volume control back and forth is a temporary fix. Radio Shack sells an electrical contact cleaner with a lubricant perfect for volume controls. This will end your problem and improve the sound. Of course this depends on the type of volume control you have. It is always a good idea to mention your equipment when asking advice.
Sim Moon I-1 Integrated Amp.

Are you taking about spraying something right into the side of the volume knob?

I think your amp has a sealed volume control. There are other problems that could cause noise while adjusting the volume. Check with the manufacturer before attempting any DIY methods.
nothing wrong w Mofimadness' advice. if its a sealed unit its probably the only thing you can do, short of sending it out for service. It cannot hurt to try the rapid rotation method, AS LONG as the unit is turned off.
Nothing wrong with Mofimadness' advice except it's not a cure. The problem will soon return and as it returns the sound is degrading. I tried the rapid rotation method on a preamp and the volume pot eventually froze up and needed to be replaced anyway. A quality properly operating volume pot is a key element to good sound.
If this is happening while you're changing the volume from your remote, the noise be caused by the little motor that is moving it, if it just happens with the remote.

I've seen some new upper-end units do this, while some cheap ones don't. It depends on the design. You could ask the company if this is normal while using the remote. If it did this since new, it just may be its design. The motor doesn't do anything (add noise), when all is well, while playing music at a fixed level.

If it does it while changing it manually by the knob, then the volume potentiometer most likely is the problem. It could be adding some noise that may not be really noticeable now. But, it can worsen, if this is the case.
Rrog, you're right. I also found rotating pot a temporary remedy on my Benchmark DAC1 volume control. I used contact cleaner/fader lube and so far it is completely silent for three years.