98 venture engine noise

When accelerating the engine is noisy. The noise could best be described as harsh, throaty, or a roar, vroooom! I just purchased this van several months ago and a new engine was supposed to have been installed. I have driven subarus my whole life and am not use to such noise. Is this normal with this size engine. To give you a better idea as to the extent of the noise: it is only noticible upon acceleration otherwise fairly quiet and a nice ride. As to the intensity of the noise, If I have the radio on medium level it will pretty much drown it out. Also could I be mistaken and the noise is coming from the transmission? Thanks for any info you can give.
Followup: Gas mileage is very good, no overheating or any signs of engine trouble, transmission shifts smoothly, engine replaced @100,000 miles currently have 106,000. The noise has been present since I have had the van.

the 3.4 will make some noise when you tromp in it and scat too. are your rpms going abnormally high . if you tromp off it it it shouldn't go above 3000rpms before it shifts out to next gear.

Thanks for the input, I will check the RPM's. I'm not use to such a heavy throaty noise upon acceleration. My car is currently in the shop to replace the rear main seal. The engine was supposed to have been replaced at 100,000 miles, but started leaking oil from the seal at about 103,000 miles. If it is a new engine I don't see how the seal could have gone bad. I hope that the engine is not defective.

did you buy from a dealer? did he document the new engine or just say it had a new engine put in? as some dealers will tell you anything to make the sale. mighty strange for a rear seal to go out after 3,000 miles.

No, I purchased it from my mechanic. In general I am fairly satisfied with the price I paid and the performance of the car. However, that seal is very suspect. I just hope it is not an indication of an internal engine problem.

if a mechanic put the motor in and it was supposed to be a new motor then he should stand behind the motor as a new one. is he charging you for the seal work? if he is then beware!!!!!! new motor my ***. if he isn't then he shouldn't and you'll have to wait and see if he continues to warrant the motor.he should warrant the motor as a new motor for so many miles.

Yes, he is charging me $400.00. I purchased the car as is -- without warranty-- trusting his honesty as to the cars condition. He has been my mechanic for 5 years and has never dealt me an unfair hand, I honestly trusted him. Any way there is nothing that I can do. I received a price quote of $850.00 from a very reputable dealer, but cannot afford it.
Unfortunately I live in the black hole of western civilization AKA Pittsburgh and do not know of another mechanic. The mileage has been good and car has been running well. If he intentionally ripped me off, good for him he can laugh all the way to the bank.
This is the first used car I have ever purchased and I have learned alot. The good news is that even if the car completely broke down tomorrow I do not have enough invested in it that it would make that much difference.

the rear main seal could have been pinched when it was put in. hey good luck