Please take a look at the ARM supplement here: http://community.arubanetworks.com/aruba/attachments/aruba/70/1204/1/ARM+Doc+Supplement.pdf
The majority of deployments do not change any of the ARM parameters besides Min and Max TX power (and of course client aware). Noise and interference are only two of the parameters that are considered in the ARM algorithm. The target channel also has to be of X better quality than the channel that it is on. There is a minimum time that an access point needs to be on a channel before considering changing to another. In addition, there are a number of times an access point needs to scan a channel before considering changing to that channel. These timers and others make it so that channel changes are not erratic and immediate, but gradual. If the noise rises above a certain level for a specific period of time it will change channels, immediately, however...
Please read the supplement to get an idea of how it works. Again, very few people if any change these parameters without TAC, because it is hard to measure over the course of a day how much of a difference they make. Two access points near to each other on the same channel, especially in the 2.4ghz spectrum is not out of the question, but likely because there are only 3 channels in the US regulatory domain. It is not something to specifically worry about. It is much less expected on the 5ghz when doing 20mhz channels.
#AP225