Root competition with the existing tree and holly will make planting this location difficult. The reduced airflow from the nearby solid fence may also affect plant health and make growth less well-balanced (more foliage would grow on the side getting more light), especially when the new plants are young and still establishing. Unfortunately, any shrub growing quickly enough to provide screening (visual, auditory, etc.) in a reasonable amount of time will outgrow the space or require one or more prunings a year (not all evergreens tolerate regular pruning), and options that grow slowly enough to better fit the space long-term will take several years to reach a size they can screen much.

With those caveats to consider, we can suggest a few options (below), but you may need to compromise on one or more of the traits you outlined as wanting, since it's unlikely any one species can provide all that you need. You didn't mention if deer enter the yard and browse, which if they do, could considerably limit your choices even further unless they can be protected with fencing or some other type of barrier to browsing. To help any new plants establish, install as young of a specimen as possible, since that will not only require a correspondingly smaller planting hole (and leave fewer roots damaged for the existing plants), but they tend to establish with less stress than older plants.

Maryland does not have many native evergreens in that size range for a partial shade site. (You didn't mention that it needed to be evergreen, but if you want sound-deadening benefits, we're assuming that not having the branches bare for about a third of the year would be preferable.)

Options for native or nearly-native shrubs:

• Summersweet (Clethra alnifolia) -- deciduous; fragrant summer flowers; may need to be watered during drought; look for varieties that are not dwarf (many popular varieties on the market are dwarf, but the wild type of this species will be among the tallest and could eventually reach 10 feet)
• Arrowwood Viburnum (Viburnum dentatum) -- deciduous; berries for the birds (if pollinated by another Arrowwood); here too, the wild type is the best candidate for reaching 8-12 feet tall (not likely much taller); Blackhaw (Viburnum prunifolium) is another possibility with more reliable height, though not as dense/wide in my experience; also deciduous
• Spicebush (Lindera benzoin) -- deciduous; subtle but colorful yellow flowers very early in spring; host plant for Spicebush Swallowtail butterfly; can get a bare bottom with age, but the fence would cover that portion of the branches
• Common Witchhazel (Hamamelis virginiana) -- deciduous; blooms in mid-autumn with a subtle fragrance; vase-shaped when mature, so will have broad branching and a narrower base
• Florida Leucothoe (Agarista populifolia) -- evergreen; hard to find locally, and while it's not native this far north (though its range does extend outside of Florida), it is typically winter-hardy here with few to no dieback problems; may need to be watered during drought; other Leucothoe are sold by area nurseries more commonly, but they stay too short to screen what you're looking for
• dwarf variety of Canadian Hemlock (Tsuga canadensis) -- evergreen, and one of the only conifers for semi-shade; be aware that heat and drought stress might make this more vulnerable to the hard-to-control pest Hemlock Woolly Adelgid; tolerates some pruning if needed to shape, but heavy pruning combined with too much shade will result in poor growth and coverage

Other shrub options:

• Illicium (Illicium, several species and hybrids) -- evergreen; looks a bit like a Rhododendron in leaf characteristics, and while some species are native in the Southeastern U.S., they are not locally native (though several are cold-hardy enough to usually be unscathed by our winters); can be hard to find locally, but more nurseries closer to the VA line are stocking a few varieties; mature height varies with cultivar; may need to be watered during drought
• Distylium (this doesn't really have a common name) -- evergreen; looks a bit like a cherrylaurel with much smaller foliage; mature height and width varies with cultivar; as with Illicium, not easy to find locally, though more nurseries are stocking a few varieties (most of which may stay too short for your needs, though); no native, but not invasive

Since they are still widely grown, you may see nurseries stocking and recommending evergreens like Privet (Ligustrum; all types) and Leatherleaf Mahonia for this type of site. While they are indeed quite tolerant of dry shade, they are both invasive in our region and should not be planted. In recent years, False Holly (Osmanthus heterophyllus) also seems to be acting invasively, spreading into woodlands from seed; otherwise, it might have been a suitable contender.

That's not an exhaustive list (particularly for deciduous options), but it's hopefully enough to get you some ideas. Give plants enough room to mature with minimal crowding, since the more space they have to fill in, the more effective each plant will be at blocking noise and a view.

Miri