While my answers might not solve your underlying problem, I’m still willing to give it a try as occasional stuttering
is quick to ruin any good experience - and I know how annoying it can be!
Let’s look at some of the possible issues and solutions.
1) The Network Adapter
You mentioned that the stuttering “only” occurs in multiplayer,
which is why I’m lead to believe that the culprit is the On-Board NIC .
In seldom cases, the NIC can suffer from overflow issues.
Although it is rare I’ve mention it first since it has a rather easy fix.
(if i remember correctly)
The problem occurs because the CPU has received an Interrupt from the NIC,
while the NIC is exhausted (mostly due to a lot of simultaneous connection)
it just won’t respond quickly enough which results in one of the CPU cores “freezing”;
and can be experienced as occasional stutter.
To test this out, all you have to do is to switch from Wireless to Wired, or from Wired to Wireless.
If you are on a Wired connection, try out Wireless or vice-versa.
2) Background Services
Games such as Battlefield 4 Beta got quite a lot of critic because of occasional stuttering,
the entire problem was their game-launcher - which opened up a Flash-based Webpage.
The flash-plugin it self was the reason so many people experienced stuttering,
to fix this issue users had to download something called Process Explorer and
Suspend the browser/flash-plugin.
The easiest way to test this out is to ensure that NO browser is running
in the background while playing the game.
If you continue to have problems, you can try out Blackviper’s solutions to
disable any service which are not required to run Windows.
I sincerely hope that either of the solutions worked for you, if not, there are still a lot of other possible solutions - so fear not, it is fixable.