Regular stuttering issues with U Boat missions add on

I have posted this issue on the Ubi forum and I'm getting no joy there and I'm desperate to sort this stuttering issue with the U Boat missions add on, it's quite annoying you see

Firstly some background.

When I played SH4 without the add on I was playing the game at 1280x1024 resolution with medium to high graphics settings activated within the game. Windows was running with max AA settings. With all this the game was running very smoothly with no issues of judder or stuttering.

After I loaded up the U Boat mission add on, and on my first look of the game I then noticed a regular stutter or pause when the game was played in the exterior positions. This pause or stutter is very short, less than half a second but is very regular. I am still experiencing this issue with the add on in vanilla mode and with TMO, plus TMO & German soundtrack, turned down the AA settings in Windows and turned down the grapphics options and I'm even running at 1024x768 resolution. Yet, I'm still experiencing this regular pause or stutter.

I'm quite baffled as to this problem and I would like any feedback from fellow players as to any similar problems or any ideas as to the issue I have

My PC spec, and I'm sure it's no dinosaur

AMD 64 X2 Dual Core 4600+ (with AMD dual core support in Windows)
ASUS A8N SLi Deluxe
ASUS EN7900GT/GTO 256Mb RAM (latest NVIDIA drivers)
2Gb Ram (paired matching 1Gb sticks)
Game played on primary slave HDD - Western Digital Raptor 74Gb (50% full)
Audigy 4 sound card

Thanks in advance