Good quality, properly formed holsters made of appropriate weights of leather to hold the form and retain the weapon properly, are quite tightly assembled and sewn. The holster is stressed at the attachment points (belt slots or loops), which aids in tensioning the holster around the handgun and maintaining a constant position on the belt. The stress applied will cause a new holster to squeak as the leather flexes and one piece rubs against another.
This will eventually stop occuring as the holster goes through the break-in period. Stretching is normal, and friction at the connection points will adjust everything to a degree. I would expect that by the time you have worn the holster for about a month you will not notice this anymore.
I make all of my holsters very tight to accomodate the normal stretching and wear that will occur in use. Otherwise, my customer is likely to find himself with a loose and sloppy fit after a period of use. I want my products to give good service for the long-term, and I have made many holsters that are still in service after 30 years or more.
If it is very troublesome to you, I suggest application of a little lanolin, rubbed into all surfaces with a soft cloth. This will immediately increase flexibility of the leather noticeably. Be careful not to over-apply, as the lanolin remains in the leather and too much will result in limpness.