I agree with many of the comments provided below; however, I wanted to interject some points and punctuate other thoughts.
1) What you are describing is known as an "incurable defect" in the industry. The noise level will vary based on morning/evening commute times as well as weather. Such a situation can be mitigated via through the use of landscaping and/or a water feature.
2) You did not provide what area of Fremont you were looking at. The individual demand of an area can also mitigate such an issue in the mind of a Buyer. For example, I live in the Mission San Jose School attendance area, which is a very sought after location for families with children due to high academic performance. At times, I can hear freeway noise from 680 when I'm outside. I have lived in my home over 20 years now. My point: location can easily override such an issue.
3) I do not agree with the notion you would automatically be taking a 10%-20% hit on market value when you sell. Assuming the "market reduction adjustment" for street noise in the area you are looking is 10%-20%, would not the current sales price logically reflect this market adjustment right now? If you believe this to be true then there is no issue. However, if you are hesitant to accept this theory then you make yet another observation, that being, the "market reduction adjustment" for this property will always be influenced by the condition of the property, location, amenities, and overall market demand. Theoretically, under a fixed market demand the adjustment remains fixed. Improve the property to mitigate the street noise (or other upgrades) and/or have a condition where market demand increases and this same adjustment improves, benefitting the Seller.