Phone keeps vibrating at random times

I have had my phone since March.  In early June it started doing this thing where it vibrates at random times throughout the day and night.  I can't determine any association between the vibrations and anything else going on with the phone.  The vibrations are brief bursts that seem to occur in pairs spaced about a minute apart.  Sometimes hours go by with no vibrations, and sometimes they seem to occur very frequently.  The phone usually becomes very slow to respond to my commands during the intervals between vibration pairs, and the apps won't behave properly.  I tried contacting Samsung customer service but they did not respond.  Has anyone else had this problem and found a way to fix it?

I don't know what a lagfix is.  Does that mean I don't have it?  So a factory reset is the thing to try I guess.

My phone is doing the same thing. I've only had it for a few days and out of the blue it starts vibrating for no reason. What do you think causes this? Its really annoying. My boyfriend got the same phone at the same time as I did and his is fine. I haven't dropped it or anything that would cause damage. I have added quite a few apps but I'm uninstalling in case they have something to do with this issue. Its a problem cause my battery life doesn't last long as it is and now with it vibrating for no reason (no reason that I can see) my battery isn't lasting long at all. I'm going to try the factory reset but I was wanting to know do I need to uninstall everything first and what do you think caused my phone to go all haywire and vibrate? Any and all help will be greatly appreciated. Thanks in advance 

I've installed alot of apps. Mostly ringtones and wallpaper and apps for pic effects and games. Do ya think that's the problem? Too many apps or bad apps or something like that?

I found that Google+ was doing exactly as you described on my Galaxy Nexus.  Settings - Vibrate ("Also vibrate when notifications are received").